Parella, J. C., "Nonwoven Technology and Wipers", paper presented at INDA-TEC 1989, presents a perceptive account of the nonwoven industry. Specifically, Parella describes and compares the four primary techniques that commercial manufacturers have focused on for producing wipes. In order of commercialization they are:
dry staple (carded, air laid, saturation or spray bonded webs made from textile fibers);
air-lay (fabric made by air laying and bonding cellulosic or synthetic pulp fibers);
melt blown (webs formed by in-line melt spinning of very fine fibers); and
spunlace (fabrics produced by hydraulic entangling of fibers).
Parella compares these primarily using the "alphabet" of consumer driven requirements for wipes: "A" for absorbency; "B" for bulk density; "C" for consistency; "D" for durability; and "P" for price.
Dry staple nonwoven wipes were acceptable in terms of A and D, but P was a premium over 100% cellulosic paper wipes. Wipes made using the air-lay process generally met consumer needs for A, B, C, and P but fell short on improving D over already available dry staple nonwoven wipes. Despite this, product acceptance was almost immediate in industrial and consumer sectors. Fabrics made from melt blown fibers exhibited outstanding oil absorbency, and aqueous absorbency was acceptable. Adsorption or entrapment is the method of absorbency employed rather than absorption into the fiber or cellulose as in the use of the dry staple or air laying techniques. B, C, D, and P were adequate but not dramatically different from prior wipes. Spunlaced fabrics were said to be "the most complete nonwoven wiper seen to date" in terms of A, B, C, and D, and P was "within the range of acceptance given the performance characteristics."
Whitehead et al. (U.S. Pat. No. 3,881,490), at column 4, line 63, through column 5, line 68) gives a respectable rendition of the air-lay technique of fabricating nonwoven wipes. However, Anderson et al. (U.S. Pat. No. 4,100,324) describes one apparent disadvantage of air lay wood pulp fiber webs, that they exhibit reduced absorbent capacity and rate (as compared to mechanically entangled webs of wood and synthetic pulp fibers) due to the adhesive used to contain the wood pulp fibers.
Stitchbonding, as a method of bonding two fabrics together to form a durable, absorbent wipe, has apparently not received the amount of attention of the wipes industry as have the above mentioned techniques. Schwartz, in U.S. Pat. No. 3,717,150, describes an absorbent stretchable diaper comprising a layer of hydrophilic material, at least one layer of hydrophobic material, stitched together with substantially non-shrinkable yarn. The hydrophilic and hydrophobic layers are maintained in contact with each other by a series of interconnected loop chains of the yarn knitted through the layers to encase the layers in a warp knitted fabric of the yarn. After being encased in the yarn the edges of the fabric are preferably covered by a border which is stitched into place to prevent the yarn from unraveling. The preferred stitch density ranges from 28 st/10 cm to about 55 st/10 cm. Schwartz notes that a greater number of stitches per unit length increases the durability of the construction but decreases its absorbency, and that when a lower stitch density is used, fibers are typically longer (typically about 9 cm) to minimize fiber loss during laundering. No mention is made of the use yarns of differing heat stability.
Two Czechoslovakian patents, 162277 (issued Nov. 15, 1976) and 193700 (published Jan. 31, 1979), relate to stitchbonded materials. The '277 patent is drawn toward a nonwoven fabric, suitable for use as a wipe, comprising base loose fibers of natural or chemical fibers having on at least one side thereof attached a layer of lintless, bonded nonwoven fabric made by the wet laid process. No mention is made of web adhesives used in the wet laid material except that "chemical binders" are used to bond the fibers together. All layers are mechanically connected together by one or more stitching yarns, none of which is disclosed as having melting point below 175.degree. C.
The '700 Czechoslovakian patent describes a stitchbonded article, the stitching yarn containing at least two yarns of differing heat stability. The products are primarily described as being useful as an underlay fabric for pile loop stitchbonded or tufted textiles, or as an inlay scrim for needlepunched fabric. The only Example pertaining to a wipe is Example 1, which describes a single batt of cotton/viscose blend weighing 350 g/m.sup.2 stitched through using two yarns: a 120 denier polyamide yarn (melting point about 220.degree. C.), and a 100 denier polypropylene yarn (melting point 160.degree.-170.degree. C.). Both yarns are threaded through the same lapping guide in threading order 1 to 1, in the chain/plain structure offset mode, with a stitch density of 50 st/10 cm. The stitched material was subjected to heat treatment via air drum dryers at a temperature of 175.degree. C. and speed of 20 m/min with following cooldown. The finished article as it appears from the technical back side is illustrated in a schematic perspective view in FIG. 1A, showing the article 10 comprised of the cotton/viscose batt 12, plain stitch 14 of polyamide yarn, and chain stitch 16 of polypropylene yarn. FIG. 1B is a schematic representation of the stitching pattern used, and also how the lapping bars or guides are threaded. No criticality is given to the stitch density, stitch gauge (as defined herein), or fibrous web composition as they relate to rate and absolute amount of water absorbency or durability of these wipes.
Ott (U.S. Pat. No. 4,675,226), describes a stitchbonded composite wiper having a middle layer of cellulose natural fibers and outer layers of either continuous filament thermoplastic fibers, meltblown thermoplastic microfibers or rayon fibers. The layers are laminated into a composite by chain stitchbonding using stitching yarn of either polyester, cotton, rayon, nylon or a blend. The stitch density (number of stitches per 10 cm in machine direction) is given as ranging from 20 to 100 st/10, with 30 st/10 cm preferred. The stitch gauge is given as ranging from 3.5 to 22 lines per inch (claim 1), or 14 to 87 gauge (needles per 10 cm), with 55 gauge (or 14 wales/in.) being preferred. No suggestion is provided for using stitching yarns of differing heat stabilities, or of the type of adhesive preferred in the cellulose fiber layers.
The manner of producing stitchbonded materials is performed by stitchbonding machines, such as that known under the trade designation "Maliwatt" as described in U.S. Pat. Nos. 2,890,579; 3,030,786; and 3,279,221. Equivalent machines, such as that known under the trade designation "Arachne" can be used for preparing the stitchbonded materials which are precursors to the articles of the present invention.
A series of patents by Zafiroglu describes nonwoven fabrics which are multi-needle stitched with an elastic yarn (U.S. Pat. Nos. 4,704,321; 4,773,238; 4,876,128; and 5,041,255).